Milton Lee, et al, in the book entitled Open Tubular Column Gas Chromatography stated on page 195, "Carrier gas flow programming is a technique that allows the carrier gas flow rate in the column to be gradually increased to reduce the analysis time and to increase the detectability of highly retained samples. It has the following advantages over constant flow GC: (a) It allows rapid elution of compounds with high boiling points at relatively low column temperatures. (b) It allows better baseline stability and extends column lifetime in comparison to temperature programming. The evaporation rate of the stationary liquid phase changes linearly with flow rate and exponentially with temperature. (c) Low-temperature GC is particularly favorable for the analysis of thermally labile compounds. (d) It is particularly favorable for open tubular column GC because the H vs. u plot is relatively flat. (e) It demands no special apparatus. It can be effectively applied with adjustment of the column inlet pressure. (f) The initial carrier gas flow rate can be restored very rapidly and, thus more chromatographic runs can be made in a given time."
Known apparatus for carrier gas flow programming includes the suggestion of Nygren et al in the Journal of Chromatography, 1976, Volume 123, pages 101-108 to use a stepper motor, oontrolled by an electronic programming unit, to rotate the valve stem of a metering valve in the side outlet of an inlet splitter of a split type capillary GC system. In 1977 Nygren et al, in the Journal of Chromatography, Volume 142, pages 109-116, described two different electronic programming units comprising digital electronic circuits. Nohl, in Chromatography Review, 1984, Volume 11, Number 3, pages 10 and 11, described a multiple chamber/solenoid valve system in the side outlet of an inlet splitter of a split type capillary GC system. Dodo et al, in The Journal of Chromatography, 1985, Volume 328, pages 49-53, described a flow controller comprising a digital electronic oircuit. Nygren et al, in Analytical Chemistry, 1985, pages 2748-2751 also described a flow controller comprising a digital electronic circuit. These digital electronic based systems have proven to be workable in flow programmed GC but are relatively expensive and especially so in low volume production. Analog electronic circuits are known to generate continuously increasing voltage outputs comprising an electrical capacitor in the feedback loop of an operational amplifier. Flow controllers are known for constant flow GC wherein the constant flow rate of the carrier gas is selected by inputting to the flow controller a constant voltage signal, e.g., the Porter Model 201-SSVB flow controller, Porter Instrument Company, Inc., Hatfield, Pa., as described in the Porter publication FM-300, dated Sept. 1985, entitled Users Manual For Porter Thermal Mass Flowmeter and Thermal Mass Flow Controller, herein fully incorporated by reference.